Liquid-crystal display

ABSTRACT

Disclosed are liquid-crystal (LC) media for use in LC displays of the PS (polymer stabilised) or PSA (polymer sustained alignment) type which contain a liquid-crystal (LC) mixture that contains one or more compounds of formula I

The present invention relates to liquid-crystal (LC) media for use in LC displays of the PS (polymer-stabilised) or PSA (polymer-sustained alignment) type. The liquid-crystal displays (LC displays) used at present are usually those of the TN (twisted nematic) type. However, these have the disadvantage of a strong viewing-angle dependence of the contrast. In addition, so-called VA (vertical alignment) displays are known which have a broader viewing angle. The LC cell of a VA display contains a layer of an LC medium between two transparent electrodes, where the LC medium usually has a negative value of the dielectric (DC) anisotropy. In the switched-off state, the molecules of the LC layer are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place. Furthermore, OCB (optically compensated bend) displays are known which are based on a birefringence effect and have an LC layer with a so-called “bend” alignment and usually positive (DC) anisotropy. On application of an electrical voltage, a realignment of the LC molecules perpendicular to the electrode surfaces takes place. In addition, OCB displays normally contain one or more birefringent optical retardation films in order to prevent undesired transparency to light of the bend cell in the dark state. OCB displays have a broader viewing angle and shorter response times compared with TN displays. Also known are IPS (in-plane switching) displays, which contain an LC layer between two substrates, only one of which has an electrode layer, usually with a comb-shaped structure. On application of a voltage, an electric field which has a significant component parallel to the LC layer is thereby generated. This causes a realignment of the LC molecules in the layer plane. Furthermore, so-called FFS (fringe-field switching) displays have been proposed (see, inter alia, S. H. Jung et al., Jpn. J. Appl. Phys., Volume 43, No. 3, 2004, 1028), which likewise contain two electrodes on the same substrate, but, in contrast to IPS displays, only one of these is in the form of a structured (comb-shaped) electrode, and the other electrode is unstructured. A strong, so-called “fringe field” is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and also a strong horizontal component. Both IPS displays and also FFS displays have a low viewing-angle dependence of the contrast.

In VA displays of the more recent type, uniform alignment of the LC molecules is restricted to a plurality of relatively small domains within the LC cell. Disclinations may exist between these domains, also known as tilt domains. VA displays having tilt domains have, compared with conventional VA displays, a greater viewing-angle independence of the contrast and the grey shades. In addition, displays of this type are simpler to produce since additional treatment of the electrode surface for uniform alignment of the molecules in the switched-on state, such as, for example, by rubbing, is no longer necessary. Instead, the preferential direction of the tilt or pretilt angle is controlled by a special design of the electrodes. In so-called MVA (multi-domain vertical alignment) displays, this is usually achieved by the electrodes having protrusions which cause a local pretilt. As a consequence, the LC molecules are aligned parallel to the electrode surfaces in different directions in different, defined regions of the cell on application of a voltage. “Controlled” switching is thereby achieved, and the formation of interfering disclination lines is prevented. Although this arrangement improves the viewing angle of the display, it results, however, in a reduction in its transparency to light. A further development of MVA uses protrusions on only one electrode side, while the opposite electrode has slits, which improves the transparency to light. The slitted electrodes generate an inhomogeneous electric field in the LC cell on application of a voltage, meaning that controlled switching is still achieved. For further improvement of the transparency to light, the separations between the slits and protrusions can be increased, but this in turn results in a lengthening of the response times. In the so-called PVA (patterned VA), protrusions are rendered completely superfluous in that both electrodes are structured by means of slits on the opposite sides, which results in increased contrast and improved transparency to light, but is technologically difficult and makes the display more sensitive to mechanical influences (tapping, etc.). For many applications, such as, for example, monitors and especially TV screens, however, a shortening of the response times and an improvement in the contrast and luminance (transmission) of the display are demanded.

A further development are the so-called PS (polymer-stabilised) displays, which are also known under the term “PSA” (polymer-sustained alignment). In these, a small amount (for example 0.3%, typically <1%) of a polymerisable compound is added to the LC medium and, after introduction into the LC cell, is polymerised or crosslinked in situ, usually by UV photopolymerisation, with an electrical voltage applied between the electrodes. The addition of polymerisable mesogenic or liquid-crystalline compounds, also known as “reactive mesogens” (RMs), to the LC mixture has proven particularly suitable.

In the meantime, the PSA principle is being used in diverse classical LC displays. Thus, for example, PSA-VA, PSA-OCB, PS-IPS/FFS and PS-TN displays are known. The polymerisation of the polymerisable compound(s) preferably takes place with an applied electrical voltage in the case of PSA-VA and PSA-OCB displays, with or without, preferably without, an applied electrical voltage in the case of PSA-IPS displays. As can be demonstrated in test cells, the PSA method results in a pretilt in the cell. In the case of PSA-OCB displays, it is therefore possible for the bend structure to be stabilised so that an offset voltage is unnecessary or can be reduced. In the case of PSA-VA displays, this pretilt has a positive effect on response times. For PSA-VA displays, a standard MVA or PVA pixel and electrode layout can be used. In addition, however, it is possible, for example, to manage with only one structured electrode side and no protrusions, which significantly simplifies production and at the same time results in very good contrast at the same time as very good transparency to light.

PSA-VA displays are described, for example, in JP 10-036847 A, EP 1 170 626 A2, EP 1 378 557 A1, EP 1 498 468 A1, US 2004/0191428 A1, US 200610066793 A1 and US 2006/0103804 A1. PSA-OCB displays are described, for example, in T.-J-Chen et al., Jpn. J. Appl. Phys. 45, 2006, 2702-2704 and S. H. Kim, L.-C-Chien, Jpn. J. Appl. Phys. 43, 2004, 7643-7647. PS-IPS displays are described, for example, in U.S. Pat. No. 6,177,972 and Appl. Phys. Lett. 1999, 75(21), 3264. PS-TN displays are described, for example, in Optics Express 2004, 12(7), 1221.

Like the conventional LC displays described above, PSA displays can be operated as active-matrix or passive-matrix displays. In the case of active-matrix displays, individual pixels are usually addressed through integrated, non-linear active elements, such as, for example, transistors (for example thin-film transistors, “TFTs”), and in the case of passive-matrix displays, they are usually addressed by the multiplex method, as known from the prior art.

In particular for monitor and especially TV applications, optimisation of the response times, but also of the contrast and luminance (thus also transmission) of the LC display continues to be demanded. The PSA method can provide crucial advantages here. In particular in the case of PSA-VA, a shortening of the response times, which correlates with a measurable pretilt in test cells, can be achieved without significant adverse effects on other parameters.

However, it has been found that the LC mixtures and RMs known from the prior art still have some disadvantages on use in PSA displays. Thus, not every desired soluble RM by far is suitable for use in PSA displays, and it is often difficult to find more suitable selection criteria than the direct PSA experiment with pretilt measurement. The choice becomes even smaller if polymerisation by means of UV light without the addition of photoinitiators is desired, which may be advantageous for certain applications. In addition, the LC mixture (also referred to as “LC host mixture” below)+polymerisable component “material system” selected should have the lowest possible rotational viscosity and the best possible electrical properties, with the emphasis here being on the so-called “voltage holding ratio” (VHR or HR). In connection with PSA displays, a high VHR after irradiation with UV light is, in particular, of central importance since UV exposure is a necessary part of the display production process, but naturally also occurs as “normal” exposure in the finished display.

However, the problem arises that not all LC mixture+polymerisable component combinations by far are suitable for PSA displays since, for example, no tilt or an inadequate tilt arises or since, for example, the VHR is inadequate for TFT display applications.

In particular, it would be desirable to have available novel materials for PSA displays which generate a particularly low pretilt angle. Materials which generate a lower pretilt angle during polymerisation for the same exposure time than the materials known to date, and/or through the use of which the (higher) pretilt angle that can be achieved using the known materials can already be achieved after a shorter exposure time would be particularly desirable. The production time (tact time) of the display could thus be shortened and the costs of the production process reduced. A faster polymerisation rate of the RM is also particularly advantageous in order, if appropriate, to enable residual amounts of unpolymerised RMs still present to react as quickly as possible after the tilt angle has been established. The presence of unreacted RMs in the display may have a disadvantageous effect on the display properties. Besides fast polymerisation of the RMs, the most complete polymerisation possible of the RMs is therefore also desirable.

There is thus still a great demand for PSA displays, in particular of the VA and OCB type, and for LC media and polymerisable compounds for use in such displays, which do not have the disadvantages described above or only do so to a small extent and have improved properties. In particular, there is a great demand for PSA displays, and for materials for use in PSA displays, which facilitate a high specific resistance at the same time as a large working-temperature range, short response times, even at low temperatures, and a low threshold voltage, a low pretilt angle, a multiplicity of grey shades, high contrast and a broad viewing angle, and have high values of the voltage holding ratio (VHR) after UV exposure.

The invention has the object of providing novel LC media for use in PSA displays which do not have the disadvantages indicated above or only do so to a reduced extent, enable a low pretilt angle to be established, and preferably at the same time facilitate very high specific resistance values, high VHR values, low threshold voltages and short response times.

This object has been achieved in accordance with the invention by LC media and LC displays as described in the present application. In particular, it has been found, surprisingly, that the use of LC media according to the invention in PSA displays facilitates particularly low pretilt angles and fast establishment of the desired tilt angles. This has been demonstrated in connection with an LC medium by means of pretilt measurements. In particular, a pretilt has been achieved without the addition of photoinitiator. In addition, the materials according to the invention exhibit significantly faster generation of the pretilt angle compared with the materials known from the prior art, as has been demonstrated by exposure time-dependent measurements of the pretilt angle. In addition, it has been found that, on use of LC media according to the invention, both the rate and completeness of the polymerisation of the RMs can be significantly increased compared with the LC media known from the prior art. This enables both a shortening of the exposure time and thus more efficient and economic performance of the process, and a reduction in the residual amount of undesired, unpolymerised RMs in the display.

The invention relates to the use of LC mixtures comprising one or more compounds of the formula I

in which the individual radicals have the following meanings:

-   R¹ and R² each, independently of one another, denote alkyl having 1     to 12 C atoms, where, in addition, one or two non-adjacent CH₂     groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such     a way that O atoms are not linked directly to one another,     preferably alkyl or alkoxy having 1 to 6 C atoms, -   A¹, A², A³, A⁴ each, independently of one another, denote

one, two or three of the radicals A¹, A², A³ and A⁴ also denote

-   L¹ and L² each, independently of one another, denote H, F, Cl, OCF₃,     CF₃, CH₂F, CHF₂, -   Z¹, Z², Z³ each, independently of one another, denote —COO—, —OCO—,     —CF₂O—, —OCF₂—, —CH₂O, —OCH₂—, —SCH₂—, —CH₂S—, —CH₂CH₂—, —C₂F₄—,     —CH₂—CF₂—, —CF₂CH₂—, —(CH₂)_(z)—, —CH═CH—, —CF═CF—, —CH═CF—,     —CF═CH—, —C≡C—, —CH═CHCH₂O—, or a single bond, where, in the case     where m=0, Z¹ and Z² do not simultaneously denote a single bond, -   z denotes 3, 4, 5 or 6, -   m denotes 0 or 1,     in LC displays of the PS (polymer stabilised) or PSA (polymer     sustained alignment) type.

The invention furthermore relates to an LC medium comprising an LC mixture according to the invention as described above and below, and one or more polymerisable compounds, preferably selected from the group consisting of reactive mesogens.

The invention furthermore relates to an LC medium comprising an LC mixture according to the invention as described above and below, and a polymer obtainable by polymerisation of one or more polymerisable compounds, which are preferably selected from the group consisting of reactive mesogens.

The invention furthermore relates to an LC medium comprising

-   -   a polymerisable component A) comprising one or more         polymerisable compounds, preferably selected from reactive         mesogens, and     -   a liquid-crystalline component B), also referred to as “LC host         mixture” below, consisting of an LC mixture according to the         invention comprising one or more compounds of the formula I as         described above and below.

The invention furthermore relates to an LC medium comprising

-   -   a polymer obtainable by polymerisation of a polymerisable         component A) comprising one or more polymerisable compounds,         preferably selected from reactive mesogens, and     -   a liquid-crystalline component B), also referred to as “LC host         mixture” below, consisting of an LC mixture according to the         invention comprising one or more compounds of the formula I as         described above and below.

The invention furthermore relates to the use of LC mixtures and LC media according to the invention in PS and PSA displays, in particular the use in PS and PSA displays containing an LC medium, for generating a tilt angle in the LC medium by in-situ polymerisation of the polymerisable compound(s) in the PSA display with application of an electric or magnetic field.

The invention furthermore relates to an LC display containing an LC medium according to the invention, in particular a PS or PSA display, particularly preferably a PSA-VA, PS-IPS or PS-FFS display.

The invention furthermore relates to an LC display of the PS or PSA type containing an LC cell consisting of two substrates, where at least one substrate is transparent to light and at least one substrate has an electrode layer, and a layer, located between the substrates, of an LC medium comprising a polymerised component and a low-molecular-weight component, where the polymerised component is obtainable by polymerisation of one or more polymerisable compounds in the LC medium between the substrates of the LC cell with application of an electrical voltage, and where the low-molecular-weight component is an LC mixture according to the invention as described above and below.

The invention furthermore relates to a process for the preparation of an LC medium according to the invention by mixing one or more low-molecular-weight liquid-crystalline compounds, or an LC mixture according to the invention, with one or more polymerisable compounds, and optionally with further liquid-crystalline compounds and/or additives.

The invention furthermore relates to a process for the production of an LC display according to the invention by mixing an LC mixture according to the invention with one or more polymerisable compounds and optionally with further liquid-crystalline compounds and/or additives, introducing the resultant mixture into an LC cell as described above and below, and polymerising the polymerisable compound(s) with application of an electrical voltage.

The following meanings apply above and below:

The term “PSA” is, unless indicated otherwise, used to represent PS displays and PSA displays.

The terms “tilt” and “tilt angle” relate to a tilted alignment of the LC molecules of an LC medium relative to the surfaces of the cell in an LC display (here preferably a PS or PSA display). The tilt angle here denotes the average angle (<90°) between the longitudinal molecular axes of the LC molecules (LC director) and the surface of the plane-parallel outer plates which form the LC cell. A low value of the tilt angle (i.e. a large deviation from the 90° angle) corresponds to a large tilt. A suitable method for measurement of the tilt angle is given in the examples. Unless indicated otherwise, tilt angle values disclosed above and below relate to this measurement method.

The term “mesogenic group” is known to the person skilled in the art and is described in the literature, and denotes a group which, due to the anisotropy of its attracting and repelling interactions, essentially contributes to causing a liquid-crystal (LC) phase in low-molecular-weight or polymeric substances. Compounds containing mesogenic groups (mesogenic compounds) do not necessarily have to have an LC phase themselves. It is also possible for mesogenic compounds to exhibit LC phase behaviour only after mixing with other compounds and/or after polymerisation. Typical mesogenic groups are, for example, rigid rod- or disc-shaped units. An overview of the terms and definitions used in connection with mesogenic or LC compounds is given in Pure Appl. Chem. 73(5), 888 (2001) and C. Tschierske, G. Pelzl, S. Diele, Angew, Chem. 2004, 116, 6340-6368,

The term “spacer group”, also referred to as “Sp” above and below, is known to the person skilled in the art and is described in the literature, see, for example, Pure Appl. Chem. 73(5), 888 (2001) and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368. Unless indicated otherwise, the term “spacer group” or “spacer” above and below denotes a flexible group which connects the mesogenic group and the polymerisable group(s) to one another in a polymerisable mesogenic compound.

The term “reactive mesogen” or “RM” denotes a compound containing a mesogenic group and one or more functional groups which are suitable for polymerisation (also referred to as polymerisable group or group P).

The terms “low-molecular-weight compound” and “unpolymerisable compound” denote compounds, usually monomeric, which contain no functional group which is suitable for polymerisation under the usual conditions known to the person skilled in the art, in particular under the conditions used for the polymerisation of RMs.

For the purposes of this invention, the term “LC medium” is intended to denote a medium which comprises an LC mixture and one or more polymerisable compounds (such as, for example, reactive mesogens). The term “LC mixture” (or “host mixture”) is intended to denote a liquid-crystalline mixture which consists exclusively of unpolymerisable, low-molecular-weight compounds, preferably of two or more liquid-crystalline compounds and optionally further additives, such as, for example, chiral dopants or stabilisers. “Unpolymerisable” means that the compounds are stable or unreactive to a polymerisation reaction, at least under the conditions used for polymerisation of the polymerisable compounds.

Particular preference is given to LC mixtures and LC media which have a nematic phase, in particular a nematic phase at room temperature.

The concentration of compounds of the formula I in the LC mixture (i.e. without the polymerisable component) is preferably 1%, particularly preferably 1 to 25%, very particularly preferably 2 to 10%.

Particular preference is given to LC mixtures and LC media comprising 1 to 5, preferably 1, 2 or 3, compounds of the formula I.

Particular preference is given to compounds of the formula I in which

-   -   L¹ and L² denote H, F or Cl,     -   Z¹, Z² and Z³ are selected from the group consisting of —COO—,         —OCO—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂— and a single bond, in         particular —COO—, —CH₂O— and a single bond,     -   Z¹ and/or Z³ denote a single bond,     -   m is 0, Z¹ denotes a single bond, and Z² is other than a single         bond,     -   m is 0 and Z² denotes —COO—,     -   m is 0 and Z² denotes —CH₂O—,     -   m is 1 and Z² denotes —COO—,     -   m is 1 and Z² denotes —CH₂O—,     -   m is 1 and Z² denotes a single bond,     -   m is 1 and Z¹, Z² and Z³ denote a single bond,     -   A¹, A², A³ and A⁴ are selected from

-   -   where L¹ and L² have the meaning indicated above and preferably         denote H or F,     -   one or more of the radicals A¹, A², A³ and A⁴, particularly         preferably at least A¹, denotes trans-1,4-cyclohexylene,         1,4-cyclohexenylene, tetrahydropyran-1,4-diyl or         tetrahydropyran-2,5-diyl,     -   R¹ and R² denote straight-chain alkyl or alkoxy having 1 to C         atoms or straight-chain alkenyl having 2 to 7 C atoms.

The compounds of the formula I are preferably selected from the group consisting of the following sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-12, preferably 1-6, C atoms, (O) denotes an oxygen atom or a single bond, (CH═CH) denotes an ethenylene group or a single bond, and L denotes H or F.

Particular preference is given to compounds selected from the group consisting of the formulae I1, I2, I3, I4, I5, I6, I7, I8 and I9, in particular those of the formula I1, I2, I3 or I4.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, n-hexyl, 2-ethylhexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl.

Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl.

Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxyethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy, n-dodecoxy.

Particularly preferred LC mixtures, LC media and LC displays are indicated below:

-   1) LC mixture or LC medium additionally comprising one or more     compounds of the formulae CY and/or PY:

-   -   in which the individual radicals have the following meanings:     -   a denotes 1 or 2,     -   b denotes 0 or 1,

-   -   R¹ and R² each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —COO— or —COO— in such a way that O atoms are not linked         directly to one another, preferably alkyl or alkoxy having 1 to         6 C atoms,     -   Z^(x) and Z^(y) each, independently of one another, denote         —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—,         —C₂F₄—, —CF═CF—, —CH═CHCH₂O— or a single bond, preferably a         single bond,     -   L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃,         CF₃, CH₃, CH₂F, CHF₂.     -   Preferably, both radicals L¹ and L² denote F or one of the         radicals L¹ and L² denotes F and the other denotes Cl, or both         radicals L³ and L⁴ denote F or one of the radicals L³ and L⁴         denotes F and the other denotes Cl.     -   The compounds of the formula CY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which a denotes 1 or 2, alkyl and alkyl* each, independently         of one another, denote a straight-chain alkyl radical having 1-6         C atoms, and alkenyl denotes a straight-chain alkenyl radical         having 2-6 C atoms, and (O) denotes an oxygen atom or a single         bond. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,         CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—         or CH₃—CH═CH—(CH₂)₂—.     -   The compounds of the formula PY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl         preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   The concentration of an individual compound of the formula CY or         PY in the LC mixture is preferably 2 to 20%.     -   The total concentration of compounds of the formulae CY and PY         in the LC mixture is preferably 1 to 90%, particularly         preferably 10 to 70%.

-   2) LC mixture or LC medium additionally comprising one or more     compounds of the following formula:

-   -   in which the individual radicals have the following meanings:

-   -   R³ and R⁴ each, independently of one another, denote alkyl         having 1 to 12 C atoms, in which, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another,     -   Z^(y) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,         —COO—, —OCO—, —C₂F₄—, —CF═CF—, —CH═CHCH₂O— or a single bond,         preferably a single bond.     -   The compounds of the formula ZK are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,         CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—         or CH₃—CH═CH—(CH₂)₂—.     -   The concentration of an individual compound of the formula ZK in         the LC mixture is preferably 2 to 20%.

-   3) LC mixture or LC medium additionally comprising one or more     compounds of the following formula:

-   -   in which the individual radicals on each occurrence, identically         or differently, have the following meanings:     -   R⁵ and R⁶ each, independently of one another, have one of the         meanings indicated above for R¹,

-   -   The compounds of the formula DK are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and         alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   Particular preference is given to compounds of the formulae DK1,         DK2, DK4 and DK5.

-   4) LC mixture or LC medium additionally comprising one or more     compounds of the following formula:

-   -   in which the individual radicals have the following meanings:

-   -   f denotes 0 or 1,     -   R¹ and R² each, independently of one another, denote alkyl         having 1 to 12 C atoms, where, in addition, one or two         non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,         —OCO— or —COO— in such a way that O atoms are not linked         directly to one another,     -   Z^(x) and Z^(y) each, independently of one another, denote         —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—,         —C₂F₄—, —CF═CF—, —CH═CHCH₂O— or a single bond, preferably a         single bond,     -   L¹ and L² each, independently of one another, denote F, Cl,         OCF₃, CF₃, CH₃, CH₂F, CHF₂.     -   Preferably, both radicals L¹ and L² denote F or one of the         radicals L¹ and L² denotes F and the other denotes Cl.     -   The compounds of the formula LY are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which R¹ has the meaning indicated above, alkyl denotes a         straight-chain alkyl radical having 1-6 C atoms, (O) denotes an         oxygen atom or a single bond, and v denotes an integer from 1         to 6. R¹ preferably denotes straight-chain alkyl having 1 to 6 C         atoms or straight-chain alkenyl having 2 to 6 C atoms, in         particular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂═CH—,         CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—,         CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.     -   The concentration of an individual compound of the formula LY in         the LC mixture is preferably 2 to 20%.

-   5) LC mixture or LC medium additionally comprising one or more     compounds selected from the group consisting of the following     formulae:

-   -   in which alkyl denotes C₁₋₆-alkyl, L^(x) denotes H or F, and X         denotes F, Cl, OCF₃, OCHF₂ or OCH═CF₂. Particular preference is         given to compounds of the formula G1 in which X denotes F.

-   6) LC mixture or LC medium additionally comprising one or more     compounds selected from the group consisting of the following     formulae:

-   -   in which R⁵ has one of the meanings indicated above for R¹,         alkyl denotes C₁₋₆-alkyl, d denotes 0 or 1, and z and m each,         independently of one another, denote an integer from 1 to 6. R⁵         in these compounds is particularly preferably C₁₋₆-alkyl or         -alkoxy or C₂₋₆-alkenyl, d is preferably 1. The LC medium         according to the invention preferably comprises one or more         compounds of the formulae given above in amounts of ≧5% by         weight.

-   7) LC mixture or LC medium additionally comprising one or more     biphenyl compounds selected from the group consisting of the     following formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and         alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   The proportion of the biphenyls of the formulae B1 to B3 in the         LC mixture is preferably at least 3% by weight, in particular         ≧5% by weight.     -   The compounds of the formula B2 are particularly preferred.     -   The compounds of the formulae B1 to B3 are preferably selected         from the group consisting of the following sub-formulae:

-   -   in which alkyl* denotes an alkyl radical having 1-6 C atoms. The         medium according to the invention particularly preferably         comprises one or more compounds of the formulae B1a and/or B2c.

-   8) LC mixture or LC medium additionally comprising one or more     terphenyl compounds of the following formula:

-   -   in which R⁵ and R⁶ each, independently of one another, have one         of the meanings indicated above for R¹, and

each, independently of one another, denote

-   -   in which L⁵ denotes F or Cl, preferably F, and L⁶ denotes F, Cl,         OCF₃, CF₃, CH₃, CH₂F or CHF₂, preferably F.     -   The compounds of the formula T are preferably selected from the         group consisting of the following sub-formulae:

-   -   in which R denotes a straight-chain alkyl or alkoxy radical         having 1-7 C atoms, R* denotes a straight-chain alkenyl radical         having 2-7 C atoms, (O) denotes an oxygen atom or a single bond,         and m denotes an integer from 1 to 6. R* preferably denotes         CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—,         CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.     -   R preferably denotes methyl, ethyl, propyl, butyl, pentyl,         hexyl, methoxy, ethoxy, propoxy, butoxy or pentoxy.     -   The LC medium according to the invention preferably comprises         the terphenyls of the formula T and the preferred sub-formulae         thereof in an amount of 2-50% by weight, in particular 5-20% by         weight.     -   Particular preference is given to compounds of the formulae T1,         T2, T3 and T21. In these compounds, R preferably denotes alkyl,         furthermore alkoxy, each having 1-5 C atoms.     -   The terphenyls are preferably employed in mixtures according to         the invention if the Δn value of the mixture is to be ≧0.1.         Preferred mixtures comprise 2-20% by weight of one or more         terphenyl compounds of the formula T, preferably selected from         the group of the compounds T1 to T22.

-   9) LC mixture or LC medium additionally comprising one or more     compounds selected from the group consisting of the following     formulae:

-   -   in which R¹ and R² have the meanings indicated above and         preferably each, independently of one another, denote         straight-chain alkyl having 1 to 6 C atoms or straight-chain         alkenyl having 2 to 6 C atoms.     -   Preferred media comprise one or more compounds selected from the         formulae O1, O3 and O4.

-   10) LC mixture or LC medium additionally comprising one or more     compounds of the following formula:

-   -   in which

-   -   R⁹ denotes H, CH₃, C₂H₅ or n-C₃H₇, (F) denotes an optional         fluorine substituent, and q denotes 1, 2 or 3, and R⁷ has one of         the meanings indicated for R¹, preferably in amounts of >3% by         weight, in particular ≧5% by weight and very particularly         preferably 5-30% by weight.     -   Particularly preferred compounds of the formula FI are selected         from the group consisting of the following sub-formulae:

-   -   in which R⁷ preferably denotes straight-chain alkyl, and R⁹         denotes CH₃, C₂H₅ or n-C₃H₇. Particular preference is given to         the compounds of the formulae FI1, FI2 and FI3.

-   11) LC mixture or LC medium additionally comprising one or more     compounds which contain a tetrahydronaphthyl or naphthyl unit, such     as, for example, the compounds selected from the group consisting of     the following formulae:

-   -   in which R¹⁰ and R¹¹ each, independently of one another, have         one of the meanings indicated for R¹, preferably denote         straight-chain alkyl or alkoxy having 1 to 6 C atoms or         straight-chain alkenyl having 2 to 6 C atoms, and Z¹ and Z²         each, independently of one another, denote —C₂H₄—, —CH═CH—,         —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CHCH₂CH₂—, —CH₂CH₂CH═CH—,         —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—, —CF═CH—, —CH═CF—,         —CH₂— or a single bond.

-   12) LC mixture or LC medium additionally comprising one or more     difluorodibenzochromans and/or chromans of the following formulae:

-   -   in which R¹¹ and R¹² each, independently of one another, have         the meanings indicated above, and c denotes 0 or 1, preferably         in amounts of 3 to 20% by weight, in particular in amounts of 3         to 15% by weight.     -   Particularly preferred compounds of the formulae BC and CR are         selected from the group consisting of the following         sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,         denote a straight-chain alkyl radical having 1-6 C atoms, and         alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and         alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,         CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or         CH₃—CH═CH—(CH₂)₂—.     -   Very particular preference is given to mixtures comprising one,         two or three compounds of the formula BC-2.

-   13) LC mixture or LC medium additionally comprising one or more     fluorinated phenanthrenes and/or dibenzofurans of the following     formulae:

-   -   in which R¹¹ and R¹² each, independently of one another, have         the meanings indicated above, b denotes 0 or 1, L denotes F, and         r denotes 1, 2 or 3.     -   Particularly preferred compounds of the formulae PH and BF are         selected from the group consisting of the following         sub-formulae:

-   -   in which R and R′ each, independently of one another, denote a         straight-chain alkyl or alkoxy radical having 1-7 C atoms.

-   14) LC mixture which comprises no compounds, in particular no     mesogenic or liquid-crystalline compounds, that contain one or more     alkenyl groups or that contain one or more alkyl groups in which one     or more CH₂ groups have been replaced by CH═CH and optionally     additionally by other groups.

-   15) LC mixture comprising one or more compounds selected from the     group consisting of formula CY in which a=1, formula PY in which b=0     and formula LY in which f=0, in a total concentration of 1 to 60%.

-   16) LC mixture comprising one or more compounds selected from the     group consisting of formula CY in which a=2 and formula PY in which     b=1, in a total concentration of 1 to 60%.

-   17) LC mixture comprising one or more compounds selected from the     group consisting of formula CY in which a=2 and R¹, R² denote an     alkyl or alkenyl group, and formula T, in a total concentration of 1     to 50%.

-   18) LC mixture comprising one or more compounds selected from the     group consisting of formulae ZK1, ZK2, ZK5, ZK6, DK1, DK2, DK4, DK5,     B1 and T1, in a total concentration of 1 to 60%.

-   19) LC mixture comprising one or more compounds of the formulae ZK1     and/or ZK2 in a total concentration of 1 to 40%.

-   20) LC mixture comprising one or more compounds selected from the     group consisting of formulae ZK3, ZK4, B2 and B3, in a total     concentration of 1 to 70%.

-   21) LC mixture comprising one or more compounds of the formula FI in     a total concentration of 1 to 25%.

-   22) LC medium in which the concentration of the polymerisable     component or component A) is ≦5%, preferably ≦1%, particularly     preferably ≦0.5%, and preferably ≧0.01%, particularly preferably     ≧0.1%.

-   23) LC medium in which the concentration of the liquid-crystalline     component (LC mixture) or component B) is ≧95%, particularly     preferably ≧99%.

-   24) LC medium which, apart from the polymerisable compounds of     component A, comprises no compounds that contain a terminal vinyloxy     group (—O—CH═CH₂).

-   25) PSA-VA display in which the pretilt angle is preferably ≦85°,     particularly preferably ≦80°.

The individual components of the preferred embodiments 1)-21) of the LC mixtures according to the invention are either known or their preparation processes can readily be derived from the prior art by the person skilled in the relevant art, since they are based on standard methods described in the literature. Corresponding compounds of the formula CY are described, for example, in EP-A-0 364 538. Corresponding compounds of the formula ZK are described, for example, in DE-A-26 36 684 and DE-A-33 21 373.

The combination of LC mixtures of the preferred embodiments 1)-21) indicated above with the polymerised compounds indicated above and below causes low threshold voltages, low rotational viscosities and very good low-temperature stabilities in the LC media according to the invention at the same time as constantly high clearing points and high HR values and allows a particularly low pretilt angle to be established quickly in PSA displays. In particular, the LC media in PSA displays exhibit significantly shortened response times, in particular also the grey-shade response times, compared with the media from the prior art.

The LC mixture preferably has a nematic phase range of at least 80 K, particularly preferably at least 100 K, and a rotational viscosity of not more than 250 mPa·s, preferably not more than 200 mPa·s, at 20° C.

In the VA-type displays according to the invention, the molecules in the layer of the LC medium in the switched-off state are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules with the longitudinal molecular axes parallel to the electrode surfaces takes place.

LC mixtures according to the invention for use in displays of the VA type have a negative dielectric anisotropy Δ∈, preferably of −0.5 to −10, in particular −2.5 to −7.5, at 20° C. and 1 kHz.

The birefringence Δn in LC mixtures according to the invention for use in displays of the VA type is preferably below 0.16, particularly preferably between 0.06 and 0.14, in particular between 0.07 and 0.12.

The LC mixtures and LC media according to the invention may also comprise further additives known to the person skilled in the art and described in the literature, such as, for example, polymerisation initiators, inhibitors, stabilisers, surface-active substances or chiral dopants. These may be polymerisable or unpolymerisable. Polymerisable additives are accordingly classed in the polymerisable component or component A). Unpolymerisable additives are accordingly classed in the LC mixture (host mixture) or the unpolymerisable component or component B).

The LC mixtures and LC media may comprise, for example, one or more chiral dopants, preferably selected from the group consisting of compounds from Table B below.

However, LC media with no chiral or optically active components are generally preferred.

Furthermore, 0 to 15%, preferably 0 to 10%, of one or more additives selected from the group comprising pleochroic dyes, nanoparticles, conductive salts, complex salts and substances for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases can be added to the LC media. Suitable and preferred conductive salts are, for example, ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. 24, 249-258, 1973). Substances of this type are described, for example, in DE-A-22 09 127, DE-A-22 40 864, DE-A-23 21 632, DE-A-23 38 281, DE-A-24 50 088, DE-A-26 37 430 and DE-A-28 53 728.

For the production of PSA displays, the polymerisable compounds are polymerised or crosslinked (if a compound contains two or more polymerisable groups) by in-situ polymerisation in the LC medium between the substrates of the LC display with application of a voltage. The polymerisation can be carried out in one step. It is also possible firstly to carry out the polymerisation in a first step with application of a voltage in order to generate a pretilt angle, and subsequently, in a second polymerisation step, to polymerise or crosslink the compounds which have not reacted in the first step without an applied voltage (end curing).

Suitable and preferred polymerisation methods are, for example, thermal or photopolymerisation, preferably photopolymerisation, in particular UV photopolymerisation. If necessary, one or more initiators may also be added here. Suitable conditions for the polymerisation, and suitable types and amounts of initiators, are known to the person skilled in the art and are described in the literature. For example, the commercially available photoinitiators Irgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure1173® (Ciba AG) are suitable for free-radical polymerisation. If an initiator is employed, its proportion is preferably 0.001 to 5%, particularly preferably 0.001 to 1%. However, the polymerisation can also be carried out without addition of an initiator. In a further preferred embodiment, the LC medium does not comprise a polymerisation initiator.

The polymerisable component A) or the LC medium may also comprise one or more stabilisers in order to prevent undesired spontaneous polymerisation of the RMs, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. For example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076, are particularly suitable. If stabilisers are employed, their proportion, based on the total amount of the RMs or the polymerisable component A), is preferably 10-10,000 ppm, particularly preferably 50-500 ppm.

The polymerisable compounds are also suitable for polymerisation without initiator, which is accompanied by considerable advantages, such as, for example, lower material costs and in particular less contamination of the LC medium by possible residual amounts of the initiator or degradation products thereof.

The LC media according to the invention for use in PSA displays preferably comprise ≦5%, particularly preferably ≦1%, very particularly preferably ≦0.5%, and preferably ≧0.01%, particularly preferably ≧0.1%, of polymerisable compounds, in particular polymerisable compounds of the formulae given above and below.

Particular preference is given to LC media comprising one, two or three polymerisable compounds.

Preference is furthermore given to achiral polymerisable compounds and to LC media in which the compounds of component A) and/or B) are selected exclusively from the group consisting of achiral compounds.

Preference is furthermore given to LC media in which the polymerisable component or component A) comprises one or more polymerisable compounds containing one polymerisable group (monoreactive) and one or more polymerisable compounds containing two or more, preferably two, polymerisable groups (di- or multireactive).

Preference is furthermore given to PSA displays and LC media in which the polymerisable component or component A) comprises exclusively polymerisable compounds containing two polymerisable groups (direactive).

The polymerisable compounds can be added individually to the LC media, but it is also possible to use mixtures comprising two or more polymerisable compounds according to the invention. In the case of polymerisation of such mixtures, copolymers are formed. The invention furthermore relates to the polymerisable mixtures mentioned above and below. The polymerisable compounds can be mesogenic or non-mesogenic. Particular preference is given to polymerisable mesogenic compounds, also known as reactive mesogens (RMs).

Suitable and preferred RMs for use in LC media and PSA displays according to the invention are described below.

In a preferred embodiment of the invention, the polymerisable compounds are selected from formula I*

R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  I*

in which the individual radicals have the following meanings:

-   R^(a) and R^(b) each, independently of one another, denote P, P-Sp-,     H, halogen, SF₅, NO₂, a carbon group or hydrocarbon group, where at     least one of the radicals R^(a) and R^(b) denotes or contains a     group P or P-Sp-, and where, if B¹ and/or B² contain a saturated C     atom, R^(a) and/or R^(b) may also denote a radical which is     spirolinked to this saturated C atom, -   P on each occurrence, identically or differently, denotes a     polymerisable group, -   Sp on each occurrence, identically or differently, denotes a spacer     group or a single bond, -   B¹ and B² each, independently of one another, denote an aromatic,     heteroaromatic, alicyclic or heterocyclic group, preferably having 4     to 25 ring atoms, which may also contain fused rings, and which may     also be mono- or polysubstituted by L, -   L denotes P-Sp-, H, OH, CH₂OH, halogen, SF₅, NO₂, a carbon group or     hydrocarbon group, -   Z^(b) on each occurrence, identically or differently, denotes —O—,     —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—,     —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—, —CF₂CH₂—, —CH₂CF₂—,     —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —CH≡C—, —CH═CH—COO—, —OCO—CH═CH—,     CR⁰R⁰⁰ or a single bond, -   R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl     having 1 to 12 C atoms, -   m denotes 0, 1, 2, 3 or 4, -   n1 denotes 1, 2, 3 or 4.

Particularly preferred compounds of the formula I* are those in which

-   R^(a) and R^(b) each, independently of one another, denote P, P-Sp-,     H, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, SF₅ or     straight-chain or branched alkyl having 1 to 25 C atoms, in which,     in addition, one or more non-adjacent CH₂ groups may each be     replaced, independently of one another, by —C(R⁰)═C(R⁰⁰)—, —C≡C—,     —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way     that O and/or S atoms are not linked directly to one another, and in     which, in addition, one or more H atoms may be replaced by F, Cl,     Br, I, CN, P or P-Sp-, where at least one of the radicals R^(a) and     R^(b) denotes or contains a group P or P-Sp-, where, if B¹ and/or B²     contain a saturated C atom, R^(a) and/or R^(b) may also denote a     radical which is spiro-linked to this saturated C atom, -   B¹ and B² each, independently of one another, denote 1,4-phenylene,     naphthalene-1,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl,     anthracene-2,7-diyl, fluorene-2,7-diyl, coumarine, flavone, where,     in addition, one or more CH groups in these groups may be replaced     by N, cyclohexane-1,4-diyl, in which, in addition, one or more     non-adjacent CH₂ groups may be replaced by O and/or S,     1,4-cyclohexenylene, bicycle[1.1.1]-pentane-1,3-diyl,     bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]-heptane-2,6-diyl,     piperidine-1,4-diyl, decahydronaphthalene-2,6-diyl,     1,2,3,4-tetrahydronaphthalene-2,6-diyl, indane-2,5-diyl or     octahydro-4,7-methanoindane-2,5-diyl, where all these groups may be     unsubstituted or mono- or polysubstituted by L, -   L denotes P, P-Sp-, OH, CH₂OH, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS,     —OCN, —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂,     optionally substituted silyl, optionally substituted aryl having 6     to 20 C atoms, or straight-chain or branched alkyl, alkoxy,     alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy     having 1 to 25 C atoms, in which, in addition, one or more H atoms     may be replaced by F, Cl, P or P-Sp-, -   P and Sp have the meanings indicated above, -   Y¹ denotes halogen, -   R^(x) denotes P, P-Sp-, H, halogen, straight-chain, branched or     cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or     more non-adjacent CH₂ groups may be replaced by —O—, —S—, —CO—,     —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not     linked directly to one another, and in which, in addition, one or     more H atoms may be replaced by F, Cl, P or P-Sp-, an optionally     substituted aryl or aryloxy group having 6 to 40 C atoms, or an     optionally substituted heteroaryl or heteroaryloxy group having 2 to     40 C atoms.

Particularly preferred compounds of the formula I* are selected from the following sub-formulae:

in which the individual radicals have the following meanings:

-   P¹ and P² each, independently of one another, denote a polymerisable     group, preferably having one of the meanings indicated above and     below for P, particularly preferably an acrylate, methacrylate,     fluoroacrylate, oxetane, vinyloxy or epoxy group, -   Sp¹ and Sp² each, independently of one another, denote a single bond     or a spacer group, preferably having one of the meanings indicated     above and below for Sp, and particularly preferably —(CH₂)_(p1)—,     —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or —(CH₂)_(p1)—O—CO—O—, in which     p1 is an integer from 1 to 12, and where the linking to the adjacent     ring in the last-mentioned groups takes place via the O atom, -   and where one or more of the radicals P¹-Sp¹- and P²-Sp²-may denote     R^(aa), with the proviso that at least one of the radicals P¹-Sp¹-     and P²-Sp²-present does not denote R^(aa), -   R^(aa) denotes H, F, Cl, CN or straight-chain or branched alkyl     having 1 to 25 C atoms, in which, in addition, one or more     non-adjacent CH₂ groups may each be replaced, independently of one     another, by C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—,     —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked     directly to one another, and in which, in addition, one or more H     atoms may be replaced by F, Cl, CN or P¹-Sp¹-, particularly     preferably straight-chain or branched, optionally mono- or     polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,     alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12     C atoms (where the alkenyl and alkynyl radicals have at least two C     atoms and the branched radicals have at least three C atoms), -   R⁰, R⁰⁰ each, independently of one another and identically or     differently on each occurrence, denote H or alkyl having 1 to 12 C     atoms, -   R^(y) and R^(z) each, independently of one another, denote H, F, CH₃     or CF₃, -   Z¹ denotes —O—, —CO—, —C(R^(y)R^(z))—, or —CF₂CF₂—, -   Z² and Z³ each, independently of one another, denote —CO—O—, —O—CO—,     —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂— or —(CH₂)_(n)—, where n is 2, 3 or 4, -   L on each occurrence, identically or differently, denotes F, Cl, CN     or straight-chain or branched, optionally mono- or polyfluorinated     alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl,     alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,     preferably F, -   L′ and L″ each, independently of one another, denote H, F or Cl, -   r denotes 0, 1, 2, 3 or 4, -   s denotes 0, 1, 2 or 3, -   t denotes 0, 1 or 2, -   x denotes 0 or 1.

In a preferred embodiment, the LC media comprise one or more, preferably exclusively, RMs selected from the group consisting of compounds of the formula I*, or sub-formulae thereof, which contain precisely one radical P-Sp- or P′-Sp¹ or P²-Sp² in which Sp or Sp¹ or Sp² denotes a single bond and precisely one radical P-Sp- or P¹-Sp¹ or P²-Sp² in which Sp or Sp¹ or Sp² is not a single bond (“monospacer compounds”).

In a further preferred embodiment of the invention, the polymerisable compounds are chiral or optically active compounds selected from formula II* (chiral RMs):

(R*—(B¹—Z^(b))_(m))_(k)-Q  II*

in which B¹, Z^(b) and m have on each occurrence, identically or differently, one of the meanings indicated in formula I*,

-   R* has on each occurrence, identically or differently, one of the     meanings indicated for R^(a) in formula I*, where R* can be chiral     or achiral, -   Q denotes a k-valent chiral group, which is optionally mono- or     polysubstituted by L, as defined in formula I*, -   k is 1, 2, 3, 4, 5 or 6,     where the compounds contain at least one radical R* or L which     denotes or contains a group P or P-Sp- as defined above.

Particularly preferred compounds of the formula II* contain a monovalent group Q of the formula III*

in which L and r have on each occurrence, identically or differently, the meanings indicated above,

-   A* and B* each, independently of one another, denote fused benzene,     cyclohexane or cyclohexene, -   t on each occurrence, identically or differently, denotes 0, 1 or 2,     and -   u on each occurrence, identically or differently, denotes 0, 1 or 2.

Particular preference is given to groups of the formula III* in which u denotes 1.

Further preferred compounds of the formula II* contain a monovalent group Q or one or more groups R* of the formula IV*

in which

-   Q¹ denotes alkylene or alkyleneoxy having 1 to 9 C atoms or a single     bond, -   Q² denotes optionally fluorinated alkyl or alkoxy having 1 to 10 C     atoms, in which, in addition, one or two non-adjacent CH₂ groups may     be replaced by —O—, —S—, —CH═CH—, —CO—, —OCO—, —COO—, —O—COO—,     —S—CO—, —CO—S— or —C≡C— in such a way that O and/or S atoms are not     linked directly to one another, -   Q³ denotes F, Cl, CN or alkyl or alkoxy as defined for Q², but     different from Q².

Preferred groups of the formula IV* are, for example, 2-butyl (=1-methylpropyl), 2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, in particular 2-methylbutyl, 2-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-hexyl, 2-octyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy, 6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3-methylvaleroyloxy, 4-methylhexanoyloxy, 2-chloropropionyloxy, 2-chloro-3-methylbutyryloxy, 2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy, 1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy, 1-butoxypropyl-2-oxy, 2-fluorooctyloxy, 2-fluorodecyloxy, 1,1,1-trifluoro-2-octyloxy, 1,1,1-trifluoro-2-octyl, 2-fluoromethyloctyloxy.

Further preferred compounds of the formula II* contain a divalent group Q of the formula V*

in which L, r, t, A* and B* have the meanings indicated above.

Further preferred compounds of the formula II* contain a divalent group Q selected from the following formulae:

in which Phe denotes phenyl, which is optionally mono- or polysubstituted by L, and R^(x) denotes F or optionally fluorinated alkyl having 1 to 4 C atoms.

Suitable chiral RMs are described, for example, in GB 2 314 839 A, U.S. Pat. No. 6,511,719, U.S. Pat. No. 7,223,450, WO 02/34739 A1, U.S. Pat. No. 7,041,345, U.S. Pat. No. 7,060,331 or U.S. Pat. No. 7,318,950. Suitable RMs containing binaphthyl groups are described, for example, in U.S. Pat. No. 6,818,261, U.S. Pat. No. 6,916,940, U.S. Pat. No. 7,318,950 and U.S. Pat. No. 7,223,450.

The chiral structural elements shown above and below and polymerisable and polymerised compounds containing such chiral structural elements can be employed in optically active form, i.e. as pure enantiomers or as any desired mixture of the two enantiomers, or alternatively as a racemate. The use of racemates is preferred. The use of racemates has some advantages over the use of pure enantiomers, such as, for example, significantly lower synthesis complexity and lower material costs. In addition, the use of racemates enables an undesired twist of the LC molecules in the LC display to be avoided.

Particularly preferred compounds of the formula II* are selected from the following sub-formulae:

in which L, P, Sp, m, r and t have the meanings indicated above, Z and A have on each occurrence, identically or differently, one of the meanings indicated for Z¹ and A¹ respectively, and t1 on each occurrence, identically or differently, denotes 0 or 1.

The term “carbon group” denotes a mono- or polyvalent organic group containing at least one carbon atom, where this either contains no further atoms (such as, for example, —C≡C—) or optionally contains one or more further atoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). The term “hydrocarbon group” denotes a carbon group which additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge.

“Halogen” denotes F, Cl, Br or I.

A carbon or hydrocarbon group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. A carbon or hydrocarbon radical having more than 3 C atoms can be straight-chain, branched and/or cyclic and may also contain spiro links or condensed rings.

The terms “alkyl”, “aryl”, “heteroaryl”, etc., also encompass polyvalent groups, for example alkylene, arylene, heteroarylene, etc.

The term “aryl” denotes an aromatic carbon group or a group derived therefrom. The term “heteroaryl” denotes “aryl” as defined above, containing one or more heteroatoms.

Preferred carbon and hydrocarbon groups are optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 25, particularly preferably 1 to 18, C atoms, optionally substituted aryl or aryloxy having 6 to 40, preferably 6 to 25, C atoms, or optionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 6 to 40, preferably 6 to 25, C atoms.

Further preferred carbon and hydrocarbon groups are C₁-C₄₀ alkyl, C₂-C₄₀ alkenyl, C₂-C₄₀ alkynyl, C₃-C₄₀ allyl, C₄-C₄₀ alkyldienyl, C₄-C₄₀ polyenyl, C₆-C₄₀ aryl, C₆-C₄₀ alkylaryl, C₆-C₄₀ arylalkyl, C₆-C₄₀ alkylaryloxy, C₄-C₄₀ arylalkyloxy, C₂-C₄₀ heteroaryl, C₄-C₄₀ cycloalkyl, C₄-C₄₀ cycloalkenyl, etc. Particular preference is given to C₁-C₂₂ alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl, C₃-C₂₂ allyl, C₄-C₂₂ alkyldienyl, C₆-C₁₂ aryl, C₆-C₂₀ arylalkyl and C₂-C₂₀ heteroaryl.

Further preferred carbon and hydrocarbon groups are straight-chain, branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25, C atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN and in which one or more non-adjacent CH₂ groups may each be replaced, independently of one another, by —C(R^(x))═C(R^(x))—, —N(R^(x))—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another.

R^(x) preferably denotes H, halogen, a straight-chain, branched or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one or more non-adjacent C atoms may be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— and in which one or more H atoms may be replaced by fluorine, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 C atoms.

Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxyethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy, n-dodecoxy, etc.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclopentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoromethyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluorohexyl, etc.

Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, etc.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl, etc.

Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxyethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy, n-dodecoxy, etc.

Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino, etc.

Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. they can contain one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently bonded (such as, for example, biphenyl), or contain a combination of fused and linked rings. Heteroaryl groups contain one or more heteroatoms, preferably selected from O, N, S and Se.

Particular preference is given to mono-, bi- or tricyclic aryl groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 2 to 25 C atoms, which optionally contain fused rings and are optionally substituted.

Preference is furthermore given to 5-, 6- or 7-membered aryl and heteroaryl groups, in which, in addition, one or more CH groups may be replaced by N, S or O in such a way that O atoms and/or S atoms are not linked directly to one another.

Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl, [1,1′:3′,1″]terphenyl-2′-yl, naphthyl, anthracene, binaphthyl, phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene, etc.

Preferred heteroaryl groups are, for example, 5-membered rings, such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole, 1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 6-membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine, or condensed groups, such as indole, isoindole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphthimidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]-thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazothiophene, or combinations of these groups. The heteroaryl groups may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.

The (non-aromatic) alicyclic and heterocyclic groups encompass both saturated rings, i.e. those containing exclusively single bonds, and also partially unsaturated rings, i.e. those which may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, O, N, S and Se.

The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane), or polycyclic, i.e. contain a plurality of rings (such as, for example, decahydronaphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 3 to 25 C atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups, in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent CH₂ groups may be replaced by —O— and/or —S—.

Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran, pyrrolidine, 6-membered groups, such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1,3-dioxane, 1,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1.1.1]-pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.

Preferred substituents are, for example, solubility-promoting groups, such as alkyl or alkoxy, electron-withdrawing groups, such as fluorine, nitro or nitrile, or substituents for increasing the glass transition temperature (Tg) in the polymer, in particular bulky groups, such as, for example, t-butyl or optionally substituted aryl groups.

Preferred substituents, also referred to as “L” above and below, are, for example, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂, in which R^(x) has the meaning indicated above, and Y¹ denotes halogen, optionally substituted silyl or aryl having 6 to 40, preferably 6 to 20, C atoms, and straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which one or more H atoms may optionally be replaced by F or Cl.

“Substituted silyl or aryl” preferably means substituted by halogen, —CN, R⁰, —OR⁰, —CO—R⁰, —CO—O—R⁰, —O—CO—R⁰ or —O—CO—O—R⁰, in which R⁰ has the meaning indicated above.

Particularly preferred substituents L are, for example, F, Cl, CN, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, furthermore phenyl.

is preferably

in which L has one of the meanings indicated above.

The polymerisable group P is a group which is suitable for a polymerisation reaction, such as, for example, free-radical or ionic chain polymerisation, polyaddition or polycondensation, or for a polymer-analogous reaction, for example addition or condensation onto a main polymer chain. Particular preference is given to groups for chain polymerisation, in particular those containing a C═C double bond or —C≡C— triple bond, and groups which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxy groups.

Preferred groups P are selected from CH₂═CW¹—COO—, CH₂═CW¹—CO—,

CH₂═CW²—(O)_(k3)—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NH—, CH₂═CW¹—CO—NH—, CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—, (CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, HO—CW²W³—, HS—CW²W³—, HW²N—, HO—CW²W³—NH—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—, CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—, Phe-CH═CH—, HOOC—, OCN— and W⁴W⁵W⁶Si—, in which W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, C₁ or CH₃, W² and W³ each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionally substituted by one or more radicals L as defined above which are different from P-Sp-, k₁, k₂ and k₃ each, independently of one another, denote 0 or 1, k₃ preferably denotes 1.

Particularly preferred groups P are CH₂═CW¹—COO—, in particular CH₂═CH—COO—, CH₂═C(CH₃)—COO— and CH₂═CF—COO—, furthermore CH₂═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH)₂CH—O—,

Very particularly preferred groups P are vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, in particular acrylate and methacrylate.

Preferred spacer groups Sp are selected from the formula Sp′-X′, so that the radical P-Sp- corresponds to the formula P-Sp′-X′-, where

-   Sp′ denotes alkylene having 1 to 20, preferably 1 to 12, C atoms,     which is optionally mono- or polysubstituted by F, Cl, Br, I or CN     and in which, in addition, one or more non-adjacent CH₂ groups may     each be replaced, independently of one another, by —O—, —S—, —NH—,     —NR⁰—, —SiR⁰⁰R⁰⁰⁰—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—,     —NR⁰⁰—O—, —O—CO—NR⁰⁰—, —NR⁰⁰—CO—NR⁰⁰—, —CH═CH— or —C≡C— in such a     way that O and/or S atoms are not linked directly to one another, -   X′ denotes —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰⁰—,     —NR⁰⁰—CO—, —NR⁰⁰—CO—NR⁰⁰, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—,     —OCF₂—, —CF₂S—, —SCF₂—, —CF₂CH₂—, —CH₂CF₂—, —CF₂CF₂—, —CH═N—,     —N═CH—, —N═N—, —CH═CR⁰—, —CY²═CY³—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—     or a single bond, -   R⁰⁰ and R⁰⁰⁰ each, independently of one another, denote H or alkyl     having 1 to 12 C atoms, and -   Y² and Y³ each, independently of one another, denote H, F, Cl or CN. -   X′ is preferably —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰—,     —NR⁰—CO—, —NR⁰—CO—NR⁰— or a single bond.

Typical spacer groups Sp′ are, for example, —(CH₂)_(p1)—, —(CH₂CH₂O)_(q1)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂—, —CH₂CH₂—NH—CH₂CH₂— or -(SiR⁰⁰R⁰⁰⁰—O)_(p1)—, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R⁰⁰ and R⁰⁰⁰ have the meanings indicated above.

Particularly preferred groups —X′-Sp′- are —(CH₂)_(p1)—, —O—(CH₂)_(p1)—, —OCO—(CH₂)_(p1)—, —OCOO—(CH₂)_(p1)—.

Particularly preferred groups Sp′ are, for example, in each case straight-chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.

In a further preferred embodiment of the invention, P-Sp- denotes a radical containing two or more polymerisable groups (multifunctional polymerisable radicals). Suitable radicals of this type and polymerisable compounds containing them and the preparation thereof are described, for example, in U.S. Pat. No. 7,060,200 B1 or US 2006/0172090 A1. Particular preference is given to multifunctional polymerisable radicals P-Sp- selected from the following formulae:

—X-alkyl-CHP¹—CH₂—CH₂P²  I*a

—X-alkyl-C(CH₂P¹)(CH₂P²)—CH₂P³  I*b

—X-alkyl-CHP¹CHP²—CH₂P³  I*c

—X-alkyl-C(CH₂P¹)(CH₂P²)—C_(aa)H_(2aa+1)  I*d

—X-alkyl-CHP¹—CH₂P²  I*e

—X-alkyl-CHP¹P¹P²  I*f

—X-alkyl-CP¹P²—C_(aa)H_(2aa+1)  I*g

—X-alkyl-C(CH₂P¹)(CH₂P²)—CH₂OCH₂—C(CH₂P³)(CH₂P⁴)CH₂P⁵  I*h

—X-alkyl-CH((CH₂)_(aa)P¹)((CH₂)_(bb)P²)  I*i

—X-alkyl-CHP¹CHP²—C_(aa)H_(2aa+1)  I*k

—X′-alkyl-C(CH₃)(CH₂P¹)(CH₂P²)  I*m

in which

-   alkyl denotes a single bond or straight-chain or branched alkylene     having 1 to 12 C atoms, in which one or more non-adjacent CH₂ groups     may each be replaced, independently of one another, by     —C(R⁰⁰)═C(R⁰⁰⁰)—, —C≡C—, —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,     —O—CO—O— in such a way that O and/or S atoms are not linked directly     to one another and in which, in addition, one or more H atoms may be     replaced by F, Cl or CN, where R⁰⁰ and R⁰⁰⁰ have the meanings     indicated above, -   aa and bb each, independently of one another, denote 0, 1, 2, 3, 4,     5 or 6, -   X has one of the meanings indicated for X′, and -   P¹⁻⁵ each, independently of one another, have one of the meanings     indicated for P.

Preference is furthermore given to compounds of the formula I* and subformulae thereof in which B¹ and/or B² denote an at least partially saturated radical, preferably cyclohexylene, in which R^(a) and/or R^(b) denote P- or P-Sp and are linked to an sp³-hybridised C atom of this radical B¹ or B² and in which this sp³-hybridised C atom contains, as further substituent, a radical P (or P^(1/2)) or P-Sp- (or P¹-Sp¹- or P²-Sp²-), which preferably has the same meaning as the radical R^(a) or R^(b) linked to the same sp³ C atom. Particularly preferred compounds contain a structural element of the formula

—C^(sp)((CH₂)_(aa)P¹)((CH₂)_(bb)P²)  I*n

in which C^(sp3) denotes the sp^(a)-hybridised C atom in the radical B¹ or B², and P¹, P², aa and bb have the meanings indicated above.

The polymerisable compounds and RMs can be prepared analogously to processes known to the person skilled in the art and described in standard works of organic chemistry, such as, for example, in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], ThiemeVerlag, Stuttgart. Further synthetic methods are given in the documents cited above and below. In the simplest case, the synthesis of such RMs is carried out, for example, by esterification or etherification of 2,6-dihydroxynaphthalene or 4,4′-dihydroxybiphenyl using corresponding acids, acid derivatives or halogenated compounds containing a group P, such as, for example, (meth)acryloyl chloride or (meth)acrylic acid, in the presence of a dehydrating reagent, such as, for example, DCC (dicyclohexylcarbodiimide).

The preparation of the LC media which can be used in accordance with the invention is carried out in a manner conventional per se, for example by mixing one or more of the above-mentioned compounds with one or more polymerisable compounds as defined above, and optionally with further liquid-crystalline compounds and/or additives. In general, the desired amount of the components used in smaller amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing. The invention furthermore relates to the process for the preparation of the LC media according to the invention.

It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl or F have been replaced by the corresponding isotopes.

The structure of the LC displays according to the invention corresponds to the usual geometry for PSA displays, as described in the prior art cited at the outset. Geometries without protrusions are preferred, in particular those in which, in addition, the electrode on the coloured-filter side is unstructured and only the electrode on the TFT side has slits. Particularly suitable and preferred electrode structures for PS-VA displays are described, for example, in US 2006/0066793 A1.

The LC mixtures and LC media according to the invention are in principle suitable for any type of PS or PSA display, in particular those based on LC media of negative dielectric anisotropy, particularly preferably for PSA-VA, PSA-IPS or PS-FFS displays. However, the person skilled in the art will also be able, without inventive step, to employ suitable LC mixtures and LC media according to the invention in other displays of the PS or PSA type, for example in PS-TN or PS-OCB displays, which differ from the above-mentioned displays, for example, through their basic structure or through the nature, arrangement or structure of the individual components used, such as, for example, the substrates, alignment layers, electrodes, addressing elements, backlighting, polarisers, coloured filters, compensation films optionally present, etc.

The following examples explain the present invention without restricting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addition, the examples illustrate the properties and property combinations that are accessible.

The following abbreviations are used:

n, m, z: in each case, independently of one another, 1, 2, 3, 4, 5 or 6)

TABLE A

In a preferred embodiment of the present invention, the LC media according to the invention comprise one or more compounds selected from the group consisting of compounds from Table A.

TABLE B Table B shows possible chiral dopants which can be added to the LC media according to the invention.

The LC media preferably comprise 0 to 10%, in particular 0.01 to 5% and particularly preferably 0.1 to 3%, of dopants. The LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table B.

TABLE C Table C shows possible stabilisers which can be added to the LC media according to the invention. (n here denotes an integer from 1 to 12)

The LC media preferably comprise 0 to 10%, in particular 1 ppm to 5% and particularly preferably 1 ppm to 1%, of stabilisers. The LC media preferably comprise one or more stabilisers selected from the group consisting of compounds from Table C.

TABLE D Table D shows illustrative compounds which can be used in the LC media in accordance with the present invention, preferably as reactive mesogenic compounds.

In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds from Table D.

In addition, the following abbreviations and symbols are used:

-   V₀ threshold voltage, capacitive [V] at 20° C., -   n_(e) extraordinary refractive index at 20° C. and 589 nm, -   n_(o) ordinary refractive index at 20° C. and 589 nm, -   Δn optical anisotropy at 20° C. and 589 nm, -   ∈_(⊥) dielectric susceptibility perpendicular to the director at     20° C. and 1 kHz, -   ∈∥ dielectric susceptibility parallel to the director at 20° C. and     1 kHz, -   Δ∈ dielectric anisotropy at 20° C. and 1 kHz, -   cl.p., T(N,I) clearing point [° C.], -   γ₁ rotational viscosity at 20° C. [mPa·s], -   K₁ elastic constant, “splay” deformation at 20° C. [pN], -   K₂ elastic constant, “twist” deformation at 20° C. [pN], -   K₃ elastic constant, “bend” deformation at 20° C. [pN], -   LTS low-temperature stability (phase), determined in test cells, -   HR₂₀ voltage holding ratio at 20° C. [%], and -   HR₁₀₀ voltage holding ratio at 100° C. [%].

Unless explicitly noted otherwise, all concentrations and % values (with the exception of the values for HR, contrast and transmission) in the present application are indicated in percent by weight and relate to the corresponding mixture as a whole comprising all solid or liquid-crystalline components, without solvent.

Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I), are indicated in degrees Celsius (° C.). m.p. denotes melting point, cl.p.=clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The data between these symbols represent the transition temperatures.

All physical properties are and have been determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., and Δn is determined at 589 nm and Δ∈ at 1 kHz, unless explicitly indicated otherwise in each case.

The term “threshold voltage” for the present invention relates to the capacitive threshold (V₀), also called the Freedericks threshold, unless explicitly indicated otherwise. In the examples, as generally usual, the optical threshold for 10% relative contrast (V₁₀) may also be indicated.

The display used for measurement of the capacitive threshold voltage consists of two plane-parallel glass outer plates at a separation of 20 μm, each of which has, on the inside, an electrode layer and an unrubbed polyimide alignment layer on top, which effect a homeotropic edge alignment of the liquid-crystal molecules.

The display or test cell used for measurement of the tilt angles consists of two plane-parallel glass outer plates at a separation of 4 μm, each of which has, on the inside, an electrode layer and a polyimide alignment layer on top, where the two polyimide layers are rubbed antiparallel to one another and effect a homeotropic edge alignment of the liquid-crystal molecules.

The polymerisable compounds are polymerised in the display or test cell by irradiation with UVA light for a pre-specified time, with a voltage simultaneously being applied to the display (usually 10 V to 30 V alternating current, 1 kHz). In the examples, unless indicated otherwise, a 28 mW/cm² mercury vapour lamp is used, and the intensity is measured using a standard UV meter (Ushio UNI meter) fitted with a 365 nm band-pass filter.

The tilt angle is determined by rotational crystal experiment (Autronic-Melchers TBA-105). A low value (i.e. a large deviation from the 90° angle) corresponds to a large tilt here.

The VHR value is measured as follows: 0.3% of a polymerisable monomeric compound is added to the LC host mixture, and the resultant mixture is introduced into TN-VHR test cells (rubbed at 90°, TN-polyimide alignment layer, layer thickness d≈4 μm). The HR value is determined after 5 min at 100° C. before and after UV exposure for 2 h (sun test) at 1 V, 60 Hz, 64 μs pulse (measuring instrument: Autronic-Melchers VHRM-105).

EXAMPLE 1

The nematic LC mixture N1 according to the invention is formulated as follows, comprising 4% of a compound of the formula I (CPGP-4-3):

CY-3-O2 19.00% cl.p. +78.0 CY-5-O2 2.00% Δn 0.0949 CCY-3-O2 11.00% Δε −3.3 CCY-3-O3 10.00% ε_(||) 3.5 CCY-4-O2 10.00% K₃/K₁ 1.07 CPY-3-O2 6.00% γ₁ 131 CCH-25 9.00% V₀ 2.17 CCH-34 9.00% BCH-32 6.00% PCH-32 14.00% CPGP-4-3 4.00%

EXAMPLE 2

The nematic LC mixture N2 according to the invention is formulated as follows, comprising 5% of a compound of the formula I (CPYP-3-2):

CY-3-O2 22.00% cl.p. +80.0 CY-5-O2 2.00% Δn 0.0960 CCY-3-O2 8.00% Δε −3.2 CCY-4-O2 4.00% ε_(||) 3.5 CPY-2-O2 6.00% K₃/K₁ 1.05 CPY-3-O2 10.00% γ₁ 120 CCH-23 22.00% V₀ 2.26 CCH-34 6.00% BCH-32 4.00% CCH-501 6.00% CCP-3-3 5.00% CPYP-3-2 5.00%

EXAMPLE 3

The nematic LC mixture N3 according to the invention is formulated as follows, comprising 7% of compounds of the formula I (CCOC-3-3, CCOC-4-3, CBC-33F):

CY-3-O4 24.00% cl.p. +76.1 CCY-3-O2 6.00% Δn 0.0945 CCY-3-O3 3.00% Δε −2.8 CCY-2-1 10.00% ε_(||) 3.5 CCY-3-1 10.00% K₃/K₁ 0.95 PYP-2-3 10.50% γ₁ 138 PYP-2-4 3.00% V₀ 2.25 CCH-34 14.50% CCH-503 7.00% CCH-501 5.00% CCOC-3-3 2.00% CCOC-4-3 3.00% CBC-33F 2.00%

EXAMPLE 4

The nematic LC mixture N4 according to the invention is formulated as follows, comprising 4% of compounds of the formula I (CCOC-3-3, CCOC-4-3):

CY-3-O2 20.00% cl.p. +76.0 CY-5-O2 9.00% Δn 0.0956 CCY-3-O3 9.00% Δε −3.2 CCY-4-O2 5.00% ε_(||) 3.5 CPY-3-O2 7.00% K₃/K₁ 1.04 PYP-2-3 3.00% γ₁ 132 PYP-2-4 5.00% V₀ 2.24 CCP-31 5.00% CCP-33 5.00% CCH-34 10.00% CCH-25 10.00% PCH-302 8.00% CCOC-3-3 2.00% CCOC-4-3 2.00%

COMPARATIVE EXAMPLE 1

The nematic LC mixture C1 is formulated as follows:

CY-3-O4 14.00% cl.p. +70.0 CY-5-O4 13.00% Δn 0.0825 CCY-3-O2 8.00% Δε −3.5 CCY-5-O2 8.00% ε_(||) 3.5 CCY-21 9.00% K₃/K₁ 1.00 CCY-31 9.00% γ₁ 141 CPY-2-O2 8.00% V₀ 2.06 CCH-501 9.00% CCH-35 14.00% PCH-53 8.00%

EXAMPLE 5

In each case, 0.3% of RM1 (biphenyl 4,4′-dimethacrylate) is added to LC mixtures N1-N4 according to the invention and to comparative mixture C1:

The resultant LC media are each introduced into VA e/o test cells as described above. With application of a voltage of 24 V (alternating current), the cells are irradiated with UV light (365 nm) having an intensity of 50 mW/cm² for various periods, causing polymerisation of the RM.

In order to determine the polymerisation rate, the residual content of unpolymerised RM1 (in % by weight) in the test cells after various exposure times is measured using the HPLC method. To this end, each mixture is polymerised in the test cell under the conditions indicated. The mixture is then rinsed out of the test cell using MEK (methyl ethyl ketone) and measured. The results are summarised in Table 1.

TABLE 1 RM content [%] Exposure time [s] LC medium 0 120 240 360 N1 + RM1 0.3000 0.2165 0.1650 0.1130 N2 + RM1 0.3000 0.1810 0.1170 0.0850 N3 + RM1 0.3000 0.1900 0.1130 0.0820 N4 + RM1 0.3000 0.1655 0.1100 0.0775 C1 + RM1 0.3000 0.2590 0.2005 0.1635

As can be seen from Table 1, only a little unpolymerised RM1 is still present in the cell after only a short time in the case of LC mixtures N1-N4 according to the invention, whereas significantly more unpolymerised RM1 is still present after the respective same exposure time in the case of comparative mixture C1. A significantly higher polymerisation rate of RM1 can be concluded therefrom in LC mixtures N1-N4 according to the invention.

Thus, for example, LC medium N1+RM1 according to the invention has a 30% lower RM residual content than comparative medium C1+RM1 after an exposure time of 6 minutes. In the case of LC media N2+RM1, N3+RM1 and N4+RM1 according to the invention, it was even possible for the RM residual content to be halved compared with comparative medium C1+RM1.

EXAMPLE 6

The LC media described in Example 5 comprising 0.3% of RM1 in LC mixtures N1-N4 or C1 are introduced into VA e/o test cells as described above. With application of a voltage of 24 V (alternating current), the cells are irradiated with UV light having a wavelength of 365 nm and an intensity of 50 mW/cm² for various periods, causing polymerisation of the RM.

For each test cell, the pretilt angle is determined as indicated above. The pretilt angle achieved in each case for the various exposure times is summarised in Table 2.

TABLE 2 LC medium Exposure time [s] Tilt [°] N1 + RM1 0 89.1 30 88.1 60 82.3 120 76.0 240 71.5 360 67.0 N2 + RM1 0 88.9 30 87.6 60 81.8 120 74.9 240 69.9 360 68.5 N3 + RM1 0 89.3 30 87.4 60 80.1 120 74.3 240 71.0 360 69.9 N4 + RM1 0 89.0 30 85.7 60 81.3 120 72.2 240 71.8 360 69.5 C1 + RM1 0 89.5 30 88.8 60 87.4 120 82.7 240 75.6 360 74.1

As can be seen from Table 2, a lower pretilt angle can be achieved with the LC media according to the invention comprising an LC mixture N1, N2, N3 or N4 according to the invention than with the LC medium comprising comparative mixture C1. Table 2 also shows that comparable pretilt angles can already be achieved after significantly shorter exposure time with LC mixtures N1-N4 according to the invention than with the LC medium comprising comparative mixture C1.

Thus, for example, comparative medium C1+RM1 exhibits a tilt angle of 82.7° after an exposure time of 120 s. By contrast, a similar tilt angle of 82.3° is achieved after only 60 s in the case of LC medium N1+RM1 according to the invention, i.e. it was possible to halve the exposure time compared with the comparative medium.

After an exposure time of 360 s, a tilt angle of 74.1° is achieved in the case of comparative medium C1+RM1. By contrast, comparable values are achieved after only 120 s, i.e. a third of the time, in the case of LC media N2+RM1, N3+RM1 and N4+RM1 according to the invention.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German application No. DE 102009018625.5, filed Apr. 23, 2009 are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. An LC display of the PS (polymer stabilised) or PSA (polymer sustained alignment) type, comprising a liquid-crystal (LC) mixture comprising one or more compounds of formula I

in which R¹ and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, A¹, A², A³, A⁴ each, independently of one another, denote

one, two or three of the radicals A¹, A², A³ and A⁴ also denote

L¹ and L² each, independently of one another, denote H, F, Cl, OCF₃, CF₃, CH₂F, or CHF₂, Z¹, Z², Z³ each, independently of one another, denote —COO—, —OCO—, —CF₂O—, —OCF₂—, —CH₂O, —OCH₂—, —SCH₂—, —CH₂S—, —CH₂CH₂—, —C₂F₄—, —CH₂—CF₂—, —CF₂CH₂—, —(CH₂)_(z)—, —CH═CH—, —CF═CF—, —CH═CF—, —CF═CH—, —C≡C—, —CH═CHCH₂O—, or a single bond, where, in the case where m=0, Z¹ and Z² do not simultaneously denote a single bond, z denotes 3, 4, 5 or 6, and m denotes 0 or
 1. 2. A display according to claim 1, wherein the compounds of formula I are selected from the group consisting of the following formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-12 C atoms, (O) denotes an oxygen atom or a single bond, (CH═CH) denotes an ethenylene group or a single bond, and L denotes H or F.
 3. A display according to claim 1, wherein the LC mixture further comprises one or more compounds of formula CY and/or PY and/or LY:

in which a denotes 1 or 2, b denotes 0 or 1, f denotes 0 or 1,

R¹ and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, Z^(x) and Z^(y) each, independently of one another, denote —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—, —CH═CHCH₂O—, or a single bond, and L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃, CF₃, CH₃, CH₂F, or CHF₂.
 4. A display according to claim 1, wherein the LC mixture further comprises one or more compounds of formula ZK:

in which

R³ and R⁴ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, and Z^(y) denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —CF═CF—, —CH═CHCH₂O— or a single bond.
 5. A display according to claim 1, wherein the LC mixture further comprises one or more compounds of formula DK:

in which R⁵ and R⁶ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another,


6. A display according to claim 1, wherein the LC mixture further comprises one or more compounds of formula T:

in which R⁵ and R⁶ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, and

each, independently of one another, denote

in which L⁵ denotes F or Cl, and L⁶ denotes F, Cl, OCF₃, CF₃, CH₃, CH₂F or CHF₂.
 7. A display according to claim 1, wherein the LC mixture comprises 1 to 25% of one or more compounds of formula I.
 8. A display according to claim 3, wherein the LC mixture comprises one or more compounds selected from the group consisting of formula CY in which a=1, formula PY in which b=0 and formula LY in which f=0, in a total concentration of 1 to 60%.
 9. A display according to claim 3, wherein the LC mixture comprises one or more compounds selected from the group consisting of formula CY in which a=2 and formula PY in which b=1, in a total concentration of 1 to 60%.
 10. A display according to claim 1, wherein the LC mixture comprises one or more compounds selected from the group consisting of formulae ZK1, ZK2, ZK5, ZK6, DK1, DK2, DK4, DK5, B1 and T1, in a total concentration of 1 to 60%

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, R denotes a straight-chain alkyl or alkoxy radical having 1-7 C atoms, (O) denotes an oxygen atom or a single bond, and m denotes an integer of 1 to
 6. 11. A display according to claim 3, wherein the LC mixture comprises one or more compounds selected from the group consisting of formula CY in which a=2 and R¹, R² denote an alkyl or alkenyl group, and formula T, in a total concentration of 1 to 50%

in which R⁶ and R⁶ each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, and

each, independently of one another, denote

in which L⁵ denotes F or Cl, and L⁶ denotes F, Cl, OCF₃, CF₃, CH₃, CH₂F or CHF₂.
 12. An LC medium comprising a polymerisable component A) comprising one or more polymerisable compounds, or a polymer obtainable by polymerisation of a polymerisable component A) comprising one or more polymerisable compounds, and a liquid-crystalline component B) comprising a liquid-crystal (LC) mixture comprising one or more compounds of formula I

in which R¹ and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, A¹, A², A³, A⁴ each, independently of one another, denote

one, two or three of the radicals A¹, A², A³ and A⁴ also denote

L¹ and L² each, independently of one another, denote H, F, Cl, OCF₃, CF₃, CH₂F, or CHF₂, Z¹, Z², Z³ each, independently of one another, denote —COO—, —OCO—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —SCH₂—, —CH₂S—, —CH₂CH₂—, —C₂F₄—, —CH₂—CF₂—, —CF₂CH₂—, —(CH₂)_(z)—, —CH═CH—, —CF═CF—, —CH═CF—, —CF═CH—, —C≡C—, —CH═CHCH₂O—, or a single bond, where, in the case where m=0, Z¹ and Z² do not simultaneously denote a single bond, z denotes 3, 4, 5 or 6, and m denotes 0 or
 1. 13. An LC medium according to claim 12, comprising a polymerisable component A) comprising one or more polymerisable compounds, and a liquid-crystalline component B) comprising a liquid-crystal (LC) mixture comprising one or more compounds of formula I.
 14. An LC medium according to claim 12, comprising a polymer obtainable by polymerisation of a polymerisable component A) comprising one or more polymerisable compounds, and a liquid-crystalline component B) comprising a liquid-crystal (LC) mixture comprising one or more compounds of formula I.
 15. A method for generating a tilt angle in an LC medium in a PS or PSA display by in-situ polymerisation of polymerisable compound(s) in the display, wherein the LC medium is according to claim 12, comprising applying an electric or magnetic field.
 16. An LC display of the PS or PSA type containing an LC medium according to claim
 12. 17. An LC display according to claim 16, which is a PSA-VA, PS-IPS or PS-FFS display.
 18. A LC display containing an LC cell containing two substrates, where at least one substrate is transparent to light and at least one substrate has an electrode layer, and a layer, located between the substrates, of an LC medium comprising a polymerised component and a low-molecular-weight component, where the polymerised component is obtainable by polymerisation of one or more polymerisable compounds in the LC medium between the substrates of the LC cell with application of an electrical voltage, and where the low-molecular-weight component is an LC mixture comprising one or more compounds of formula I

in which R¹ and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, A¹, A², A³, A⁴ each, independently of one another, denote

one, two or three of the radicals A¹, A², A³ and A⁴ also denote

L¹ and L² each, independently of one another, denote H, F, Cl, OCF₃, CF₃, CH₂F, or CHF₂, Z¹, Z², Z³ each, independently of one another, denote —COO—, —OCO—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —SCH₂—, —CH₂S—, —CH₂CH₂—, —C₂F₄—, —CH₂—CF₂—, —CF₂CH₂—, —(CH₂)_(z)—, —CH═CH—, —CF═CF—, —CH═CF—, —CF═CH—, —C≡C—, —CH═CHCH₂O—, or a single bond, where, in the case where m=0, Z¹ and Z² do not simultaneously denote a single bond, z denotes 3, 4, 5 or 6, and m denotes 0 or
 1. 19. A process for the production of an LC display according to claim 18, comprising mixing the LC mixture comprising one or more compounds of formula I with one or more polymerisable compounds and optionally with further liquid-crystalline compounds and/or additives, introducing the resultant mixture into an LC cell, and polymerising the polymerisable compound(s) with application of an electrical voltage.
 20. A display according to claim 1, wherein the LC mixture further comprises a polymerisable component which comprises one or more polymerisable compounds of formula I* R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  I* in which R^(a) and R^(b) each, independently of one another, denote P, P-Sp-, H, halogen, SF₅, NO₂, a carbon group or hydrocarbon group, where at least one of the radicals R^(a) and R^(b) denotes or contains a group P or P-Sp-, P on each occurrence, identically or differently, denotes a polymerisable group, Sp on each occurrence, identically or differently, denotes a spacer group or a single bond, B¹ and B² each, independently of one another, denote an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may also contain fused rings, and which may also be mono- or polysubstituted by L, L denotes P-Sp-, H, OH, CH₂OH, halogen, SF₅, NO₂, a carbon group or hydrocarbon group, Z^(b) on each occurrence, identically or differently, denotes —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—, —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —CH═CH—COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single bond, R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl having 1 to 12 C atoms, m denotes 0, 1, 2, 3 or 4, and n1 denotes 1, 2, 3 or
 4. 21. A display according to claim 20, wherein the concentration of the polymerisable component is ≦5% and ≧0.01%.
 22. An LC medium according to claim 12, wherein the polymerisable component comprises one or more polymerisable compounds of formula I* R^(a)—B¹—(Z^(b)—B²)_(m)—R^(b)  I* in which R^(a) and R^(b) each, independently of one another, denote P, P-Sp-, H, halogen, SF₅, NO₂, a carbon group or hydrocarbon group, where at least one of the radicals R^(a) and R^(b) denotes or contains a group P or P-Sp-, P on each occurrence, identically or differently, denotes a polymerisable group, Sp on each occurrence, identically or differently, denotes a spacer group or a single bond, B¹ and B² each, independently of one another, denote an aromatic, heteroaromatic, alicyclic or heterocyclic group, which may also contain fused rings, and which may also be mono- or polysubstituted by L, L denotes P-Sp-, H, OH, CH₂OH, halogen, SF₅, NO₂, a carbon group or hydrocarbon group, Z^(b) on each occurrence, identically or differently, denotes —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —(CH₂)_(n1)—, —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single bond, R⁰ and R⁰⁰ each, independently of one another, denote H or alkyl having 1 to 12 C atoms, m denotes 0, 1, 2, 3 or 4, and n1 denotes 1, 2, 3 or
 4. 23. An LC medium according to claim 12, wherein the concentration of the polymerisable component is ≦5% and ≧0.01%.
 24. A display according to claim 1, wherein R¹ and R² each, independently of one another, denote alkyl or alkoxy having 1 to 6 C atoms. 